| The crib retaining structures made of wooden/bamboo logs with live plants inside are called
vegetative crib walls which are now becoming popular due to their advantages over
conventional civil engineering walls. Conventionally, wooden crib walls were dimensioned
based on past experiences. At present, there are several guidelines and design standards for
machine finished wooden crib walls, but only few guidelines for the design and construction
of vegetative log crib walls are available which are generally not sufficient for an economic
engineering design of such walls. Analytical methods are generally used to determine the
strength of vegetated crib retaining walls. The crib construction is analysed statically by
satisfying the condition of static equilibrium with acceptable level of safety. The crib wall
system is checked for internal and external stability using conventional monolithic and silo
theories.
Due to limitations of available theories, the exact calculation of the strength of vegetated
wooden/bamboo crib wall cannot be made in static calculation. Therefore, experimental
measurements are generally done to verify the static analysis. In this work, a model crib
construction (1:20) made of bamboo elements is tested in the centrifuge machine to
determine the strength behaviour of the slope supported by vegetated crib retaining
wall.
A geotechnical centrifuge is used to conduct model tests to study geotechnical problems
such as the strength, stiffness and bearing capacity of different structures, settlement of
embankments, stability of slopes, earth retaining structures etc. Centrifuge model testing is
particularly well suited to modelling geotechnical events because the increase in gravitational
force creates stresses in the model that are equivalent to the much larger prototype and
hence ensures that the mechanisms of ground movements observed in the tests
are realistic. Centrifuge model testing provides data to improve our understanding
of basic mechanisms of deformation and failure and provides benchmarks useful
for verification of numerical models. In this case this test is mainly carried out
to verify the stability analysis and deformation characteristics of a bamboo crib
wall.
Models of crib wall of dimensions 37x13x10 cm and 37x13x14cm were placed
inside a Plexiglas box of internal dimensions of 42.5x42.5x30 cm and slope was
formed leaving a space about 10 cm in the front. The model crib wall tests were all
performed at 40-70 times earth’s gravity. This means that the 5 mm diameters bamboo
rods in model used represents a prototype diameter of 20-35 cm. The horizontal
and vertical displacements were measured with the help of three displacements
sensor fixed horizontally and one sensor fixed vertically at the top of the model crib
wall.
All together nine tests were carried out with varying model parameters. Standard medium
sand and coarse sand were used as fill material in the testing. Two wall heights variations and
three slopes variations were used in the testing. The test model was constructed either
compacted or uncompacted. The compaction in the model was carried out by hand to about
90% of the Proctor density. Three slopes inclinations were used. For flat slope the slope angle
was less than 25Ë , and for steep slope it was 25Ë -35Ë and for extremely steep
slope it was > 35Ë . The test results and conclusions are presented in this paper. |